This invention relates to transparent dentifrices having high transparency and appropriate fluidity.
Transparent dentifrices are becoming more popular because of their transparent appearance. Dentifrices have a higher degree of transparency are desirable to meet the current satisfaction of consumers. A variety of proposals have heretofore been made to increase the transparency of transparent dentifrices. Most of the past transparency improvements are based on the development of abrasives including aluminosilicate (Japanese Patent Application Kokai No. 47-39643), silica (Japanese Patent Publication No. 50-899), precipitated silica (Japanese Patent Application Kokai No. 49-80256), and silica xerogel (Japanese Patent Application Kakai No. 48-49936). In addition, it was also proposed to add laponite to the vehicle in order to increase transparency (Japanese Patent Application Kokai No. 47-11150).
As is well known in the art, usual transparent dentifrices contain sodium carboxymethylcellulose (to be abbreviated as CMC-Na, hereinafter) in the vehicle as a binding agent. We have discovered that CMC-Na's commonly used as the binder in dentifrices cause turbidity when blended in transparent dentifrices. Even though the transparency of an abrasive itself is improved by a successful abrasive development or an additive regarded as effective in transparency improvement is added, the transparency of transparent dentifrices is improved only to a limited extent as long as CMC-Na is utilized.
U.S. Pat. No. 3,934,000 discloses a transparent toothpaste containing 0.2 to 2% of sodium carboxymethylcellulose (CMC-Na) having about 0.6 to 0.8 carboxymethyl groups per anhydroglucose unit. According to this patent, CMC-Na in its particularly preferred form has an average degree of polymerization in the neighborhood of 500, corresponding to a molecular weight in the neighborhood of 100,000. For instance one may use a material whose viscosity (of a 2% aqueous solution thereof at 25.degree. C.) is less than 3,000 centipoises, preferably below 1,000, e.g. about 300 to 600 centipoises, such as Hercules CMC-7MXF which has about 0.7 sodium carboxymethyl groups per anhydroglucose unit. It should be noted that a viscosity of 300 centipoises measured as 2 % aqueous solution of CMC-Na at 25.degree. C. corresponds to a viscosity of about 43 centipoises measured as 1% aqueous solution of CMC-Na at 25.degree. C.
U.S. Pat. No. 4,294,894 discloses a transparent toothpaste containing sodium chloride in amounts ranging from 0.5 to 20% by weight of the toothpaste.
There is a need for further increasing the transparency of transparent dentifrices by eliminating the turbidity of transparent dentifrices associated with the use of CMC-Na as a binding agent.